1. Field of the Invention
The present invention relates to inkjet recording systems and recording apparatuses having excellent ink chargeability.
2. Description of Related Art
Recent outstanding improvement in inkjet recording technique has enabled production of high-definition images which are very similar to photographs. Consequently, inkjet recording has been widely used in various fields of art. In association with this, there is a need of improving printing speed as well as obtaining high-definition images. As a measure for improving printing speed, there is known a method of increasing the number of nozzles, and discharging ink droplet in larger amount per unit time from each head. In such a measure, driving frequency of 15 kHz or higher is desired, and it is necessary to supply ink that is to be used in unit time by every head without any excess and deficiency from an ink cartridge.
However, in an inkjet head, when wettability of ink flow channel provided in the head is poor, bubbles may occur in the ink flow channel during charging of ink. Furthermore, these bubbles can solidly adhere to the wall face of the flow channel, and will not be discharged easily even if discharging operation by suction of ink is conducted. When bubbles remain in the ink flow channel, troubles such as dot missing and printing disorder, as well as jet impossibility occur, to deteriorate the printing quality.
In order to improve the wettability of a head constituting member made of a resin material, Japanese Patent No. 3454514 publication proposes techniques of imparting hydrophilicity by acid treatment or plasma treatment, or of containing a filler imparted with hydrophilicity by acid treatment. However, in the structure disclosed in the patent document in which ink directly contacts piezoelectric elements, piezoelectric elements may get corroded or deteriorated by hydrophilizing treatment.
On the other hand, Japanese Patent Application Laid-Open Publication No. 2004-114308 proposes a method of forming each layer by burning in a laminate-type piezoelectric element so as to increase the toughness and strength of the piezoelectric element. Since the piezoelectric element disclosed in the patent document is a burnt member of ceramics or the like, its surface has fine bumpy structure, so that ink is difficult to be charged. When bubbles remain on the surface of the piezoelectric element that generates pressure due to failure in charging of ink, the generated pressure will not travel satisfactorily, so that discharge defects such as ink flight curve, decrease in discharging speed, or discharge failure will occur.
Moreover, inventor's detailed examination of the process in which ink is charged revealed that charging ratio increases with the lapse of time, or in other words, some time is required from charging for achieving stabilization. Here, the term charging ratio means a ratio of number of nozzles capable of printing, relative to the total number of nozzles of the inkjet recording head.